A device that utilizes a source synchronous interface provides a reference signal along with data sent from the device. The reference signal is generally referred to as a strobe signal or a data strobe (DQS) signal. One example of a source synchronous device is a synchronous dynamic random access memory (SDRAM) device. The reference signal sent from the source synchronous device (source) is used by a receiving device (target) that is coupled to the source. For example, once synchronized, the target can capture data detected on the data lines from the source on the rising and/or the falling edges of the strobe signal.
At times, however, the strobe signal from the source is placed in a tri-state mode. When tri-stated, the target does not utilize the strobe signal. Moreover, the target must prevent the strobe signal sent from the source from propagating to other components or subsystems within the target since the strobe signal is essentially in an unknown or random state. According, the target must monitor the strobe signal to determine when the strobe signal is no longer tri-stated and has transitioned to providing a valid reference signal.
Determining when the strobe signal is valid within the target, however, can be difficult due to a number of factors that influence the timing of the strobe signal as received within the target. For example, one factor is that the distance traveled by the strobe signal between source and target is not known until the circuit board of a system is designed. Other factors include varying behaviors or performance characteristics of different IC sources and temperature and/or voltage variation in the source, the target, and/or the circuit board upon which the source and/or target are disposed.